1. Field of the Invention
The present invention relates to a display, and more particularly, to a flat panel display having a wide display area at least partially impervious to degradation caused by moisture.
2. Description of the Related Art
Flat panel displays, such as liquid crystal displays, organic electroluminescent displays, and inorganic electroluminescent displays can be classified as either Passive Matrix (PM) displays and Active Matrix (AM) displays according to the driving method thereof. In the PM display, positive electrodes and negative electrodes are arranged in columns and rows, and scanning signals are supplied to the negative electrodes from a row driving circuit. One row is selected. In addition, data signals are converted into pixels by a column driving circuit. In the AM display, signals converted into pixels are controlled by a Thin Film Transistor (TFT). The AM display is suitable for processing an enormous amount of data and for displaying moving pictures.
An organic Electroluminescent (EL) display has an organic light emitting layer of an organic material arranged between an anode and a cathode. In the organic EL display, when a voltage is applied across the electrodes, holes move from the anode through a hole transport layer into an organic light emitting layer, and electrons move through an electron transport layer into the organic light emitting layer. The electrons and holes recombine in the organic light emitting layer to form exitons, and when the exitons dexcite, fluorescent molecules in the organic light emitting layer emit light to form an image. In a full-color organic EL display, pixels for generating Red (R), Green (G), and Blue (B) colors are used to realize full-color.
However, in the organic EL display, organic layers including the organic light emitting layer are very vulnerable to moisture. Thus, in order to protect the organic light emitting layer from moisture and to protect a display area of the display from external shock, the layers are sealed using a substrate or a metal cap.
FIG. 1A is a plan view of an AM organic EL display, and FIG. 1B is a cross-sectional view taken along line I-I of FIG. 1.
The AM organic EL display includes a predetermined area 20 that includes an organic EL device on a transparent base substrate 11, and a metal cap 90 that is sealed by a sealing portion 80 comprising a sealant 81 arranged on the display area 20 so as to seal the display area 20. The display area 20 includes a plurality of pixels, each of which includes the organic EL device having a TFT. In addition, a cathode 40 is arranged on an upper portion of the display area 20, and the cathode 40 is connected to an external terminal area 70 through an electrode routing unit 41 that is arranged on one side of the display area 20. Also, a plurality of driving lines (VDDs) 31 are arranged on the display area 20 and connected to the external terminal area 70 through a driving voltage routing unit 30 arranged on an outer portion of the display area 20. The VDDs supply driving voltage to the display area 20. A vertical circuit unit 50 and a horizontal circuit unit 60, which input signals to the TFT of the display area 20, are further arranged on an outer portion of the display area and are connected to the terminal area 70 through circuit routing units 51 and 62.
In the AM organic EL display described above, the metal cap 90 seals a portion including the display area 20, the routing units 51 and 61, and the circuit units 50 and 60, and excluding only the terminal area 70. Therefore, the sealing portion 80 includes the routing units 51 and 61 and the circuit units 50 and 60 which do not display images, as well as the display area 20 on which images are displayed. Thus, a proportion of the display area 20 that emits light is reduced with respect to the entire size of the display, and accordingly, a dead space, that is, a non-emitting area increases, thereby lowering efficiency.
Moreover, in the organic EL display of FIGS. 1A and 1B, since widths of the routing units 51 and 61 that connect the display area 20 and the terminal area 70 must be thin, the resistance of the routing units is inevitably increased.
The above problem generally occurs in conventional AM type organic EL displays, including the organic EL display of Japanese Laid-Open Patent No. 2000-173779.
On the other hand, U.S. Pat. No. 6,359,606 refers to a technology that forms a protection layer for sealing an entire surface of the display, instead of using a sealing member such as the metal cap or a glass substrate. Thus, the protection layer, instead of the sealing member, protects and preserves the organic EL device by keeping out moisture and oxygen.
However, in the AM display described above, the protection layer is just a thin film, so internal devices are not protected sufficiently. In addition, there is a limit to the protection provided by the protection layer to the organic EL device, which should be protected completely from moisture.
U.S. Pat. No. 5,882,761 refers to a display that further includes a drying substance in the metal cap or glass substrate in order to further protect the organic EL device from moisture. Moreover, the display having the thin protection layer cannot be a front-emission display or a dual-emission display, which form images in a direction of the sealing member.
Korean Laid-open Patent Publication No. 2002-9498 refers to a display in which an EL device is sealed using a covering member and a sealing member including a plurality of wires connected to each other in parallel between the sealing member and the substrate. However, in order to manufacture the display, a plurality of wires having narrow widths must be formed and connected in parallel. Thus, the apparatus has a complex structure and a high line resistance.